1. Field of the Invention
This invention relates to an improvement in the pressure regulator of the type in which the pressure of a fluid on the secondary side of the regulator is maintained at a desired set value regardless of changes in the pressure on the primary side, wherein the improved pressure regulator has, in addition to the aforesaid capability, the capability of automatically compensating said set pressure value in response to changes in the temperature of the fluid so as to maintain constant the quality of a viscous fluid (such as paint) delivered by the regulator.
2. Description of the Prior Art
When, for example, a liquid paint is delivered under pressure to a spray gun for carrying out spray painting, it is common to provide a pressure regulator in the pressurized paint supply line. In this case, since the viscosity of the paint differs with temperature, causing variation in the supply line resistance, the quantity of paint delivered by the regulator will differ at different temperatures if the pressure of the paint on the secondary side is maintained constant. Therefore, in order to maintain a constant supply of paint from the regulator, it has been necessary to regulate the set pressure value of the fluid on the secondary side each time the temperature of the paint changes.
Conventionally, there have been known regulators designed to carry out this regulation automatically through the use of an adjustment mechanism operated by the volumetric change with temperature of a liquid having a large coefficient of thermal expansion, such as alcohol or ether. Such regulators are, however, disadvantageous in that the coefficients of expansion of alcohol, ether and the like are not large enough to cope with large fluctuations in temperature and also in that such liquids are unable to supply adequate power for operating the adjustment mechanism. Moreover, the use of an expanding liquid necessitates the utilization of an arrangement wherein the adjustment mechanism is operated by the movement of a piston rod driven by a piston which in turn is driven by the volumetric change in the liquid with temperature. This means that it is necessary to maintain a cylinder filled with liquid in air-tight condition at all times. With repeated use, however, there arises the danger of the liquid leaking out from gaps developing around the opening through which the piston rod protrudes and it is extremely difficult to provide a perfectly leak-proof structure. The conventional arrangement also creates problems regarding maintenance since any leakage that does occur may lead to an explosion or fire.
Also, most of these conventional pressure regulators employ a diaphragm on which a force is brought to bear by some means or other so as to regulate the pressure of the fluid being passed through the regulator. As a consequence, the operational sensitivity of this diaphragm determines the precision of the pressure regulator as a whole and is critical in determining whether or not the regulator is able to fulfill its purpose sufficiently and reliably. In some cases, depending on the purpose and type of the regulator, the most effective results are obtained with a diaphragm of very small area. From the points of structure and fabrication, however, it is frequently impossible to reduce the area of the diaphragm to the desired degree or, when the area is reduced, the diaphragm is found to entail so many problems regarding service life and sensitivity that it is not practical for use.